Optimal growth and PHB accumulation in Bacillus megaterium occurred with 5% (w/v) date syrup or beet molasses supplemented with NH4Cl. When date syrup and beet molasses were used alone without an additional nitrogen source, a cell density of about 3 g l(-1) with a PHB content of the cells of 50% (w/w) was achieved. NH4NO3 followed by ammonium acetate and then NH4Cl supported cell growth up to 4.8 g l(-1), whereas PHB accumulation was increased with NH4Cl followed by ammonium acetate, NH4NO3 and then (NH4)(2)SO4 to a PHB content of nearly 42% (w/w). Cultivation of B. megaterium at 30 l scale gave a PHB content of 25% (w/w) of the cells and a cell density of 3.4 g l(-1) after 14 h growth.